Understanding the end of the remaining US-Russia nuclear arms control treaty

The last remaining US-Russia nuclear arms control treaty, New START, expired on Thursday, leaving the world's two largest nuclear arsenals without legal limits on nukes for the first time in over half a century. While the US and Russia still possess the most nuclear warheads, some US policymakers argue the treaty was outdated because of China's own rapidly expanding stockpile. The World's Host Marco Werman turned to Heather Williams, director of the Project on Nuclear Issues at the Center for Strategic and International Studies, to understand what happens next.